Connectors used for connecting electric circuits in automobiles are required to have high waterproofness as well as oil resistance. Therefore, many sealing rubber parts used for the connectors, such as packing and rubber stoppers, are made of oil-bleeding rubber materials. Examples of oil-bleeding rubber sealing compounds include oil-bleeding acrylonitrile-butadiene rubber (NBR) containing an aliphatic hydrocarbon oil (JP-A-61-21177, the term "JP-A" as used herein means an "unexamined published Japanese patent application"), oil-bleeding silicone rubber containing silicone oil (JP-A-62-252457), and oil-bleeding polyolefin rubber containing an ester type plasticizer (JP-A-63-309542).
However, the conventional oil-bleeding rubber materials have their several disadvantages. That is, the NBR-based material, though inexpensive and oil-resistant, has insufficient heat resistance for application in a high temperature part of an engine room. The silicone rubber-based material is excellent in heat resistance, cold resistance and oil resistance, but is expensive resulting in limited applicability. The polyolefin-based material has insufficient oil resistance for use in an engine room.
It is impossible to reduce the cost of silicone rubber itself while retaining its excellent characteristics. Hence, various studies have been directed to reduction of molding time for rubber parts to thereby reducing the unit price of the product. Millable silicone rubber generally uses an organic peroxide as a vulcanizing agent. While silicone rubber compounds of this type have satisfactory storage stability, a long pot life, and ease in handling, they need a long vulcanizing time, failing to reduce the processing time.
On the other hand, a two-part type liquid silicone rubber compound which undergoes vulcanization on addition reaction in the presence of a platinum catalyst has recently been developed and extending its use broadly. Vulcanizable in a markedly reduced time, the addition reactive liquid silicone rubber compound is effective for reduction of molding time. However, by the nature of two-part liquid system, a mixture of the two parts must be injected into a mold immediately after mixing, making the handling complicated and requires new molding equipment.
In order to solve these problems, it has been proposed to use, as a vulcanizing agent for addition reactive millable silicone rubber compounds, fine particles comprising a platinum catalyst and a phenyl-containing silicone resin. Nevertheless, the silicone resin fine particles are easily soluble in a phenyl-containing diorganopolysiloxane having a low degree of polymerization so that they fail to manifest their merits when added to an oil-bleeding rubber material containing a phenyl-containing diorganopolysiloxane having a low degree of polymerization.